1. Field of the Invention
This invention relates to three dimensional pin impression screens.
2. Description of Related Art
The three dimensional image forming pin screen is very familiar to the general public. In the last 27 years there have been a number of variations on it.
The inventor's first exposure to pin screens was encountering a display in the Science Center of Minnesota in the summer of 1971. This display had a single perforated metal plate in a frame approximately 20" by 40" laying horizontal and supported by pillars above a pedestal. A clear cover was over the top of the unit and lay parallel to the surface of pin heads about 3/4" above them. The pins heads rested against the perforated plate and their shanks protruded about 11/2" below. Pushing from underneath with a hand reproduced an image of the hand in the pins above. This pin screen and a version manufactured later by Ballantine & Co. ( Art in America, p.141, July 1978) only retained the image if the object was pressed into the pins. Work earlier by Alexeieff & Parker ( ASIFI Information Bulletin, pp. 90-99, 1972) and discussed later by Laybourne (The Animation Book, pp. 152-154, 1979) used a vertical pin screen. This device had a second axially aligned perforated plate mounted parallel to the first. Provided they were not pushed beyond the apertures of the plates, these pins remained horizontal.
This device was able to produce an image used for animation art. The pins were capable of movement of a few millimeters, their black heads being located varying distances from the white background of the first perforated plate they were inserted into. This produced a gray scale image caused by the density of the pins against the white background. This contrast was not attributed to the shadows caused by light striking the pins.
U.S. Pat. No. 4,654,989 to Fleming (1987) was a variation in which a transparent plate was placed a spaced distance from the heads of the pins in the front perforated plate and the pins were of such length that when their heads contacted the inside surface of the transparent plate, a short section of their shanks still protruded from the back of the rear perforated plate. The pins were thus prevented from falling out of their places in the perforated plates completely.
A three dimensional image could be made with the pin screen in a horizontal orientation as in the earliest prior art discussed. This image remained only when the object creating it still pressed against the surface of the pin ends. The pin screen could also be set up vertically and an impression made by horizontally pressing an object into the surface of the ends of the pins protruding from the rear perforated plate of the device. This impression would remain even after the object was removed, provided the pin positions were not disturbed. Unfortunately, it was easy to disturb those impressions by shaking the device lightly or tipping it away from the vertical. The inventor recalls many individuals wishing that a more permanent yet easily corrected or altered impression was possible.
The inventor (1995) had occasion to make a large pin screen for a non-profit science center in which the prototype had a movable transparent plate between the fixed transparent plate and the heads of the pins. This allowed the pin screen to be reset while still in a vertical position. This arrangement only allowed for small corrections in an impression. It was possible to slip a small thin tool between the movable plate and the heads of the pins and push the pins back to a different position provided no other pins were in the way.
Gauge pin arrays which are similar to pin screens have been used to measure the contours of feet for the production of inner soles. These arrays produce a three dimensional impression. U.S. Pat. No. 4,454,618 to Curchod (1984) solves the problem of retention of pins in a displaced position in the gauge pin array by utilizing an inflatable tube which presses against retaining strips that communicates that pressure to floating wedges capable of pressing against the shanks of the pins. The pneumatic device is costly and does not lend itself to being easily employed in a pin array with pin spacing 1/16" or less. The pin spacing in the Curchod device is approximately 1/41" to 3/841 .
Similarly, U.S. Pat. No. 4,876,758 to Rolloff (1989) and U.S. Pat. No. 5,689,446 to Sundman et al. (1997) still use retention devices which require enough space between the pins to insert inflatable rubber tubing to put retention pressure on the pin shanks. All of these devices use an inflatable diaphragm to push against the heads of the pins. Such diaphragms are not suited for the movement of single or small groups of pins a great distance or the creation of narrow lines or forms as would be possible using a card or a form such as a cookie cutter. Prior art U.S. Pat. No. 5,092,591 to Tol (1992) similarly uses a rubber element which is clamped around a large pin to restrict its movement. It also is not practical for very small pin spacing.
Other prior art includes picture toy devices as in U.S. Pat. No. 3,568,357 to Lebensfeld (1971), UK Patent Application 2,037,471 of Li (1980) , and U.S. Pat. No. 5,391,105 to Jones (1995). Lebensfeld uses removable light conducting pegs and a perforated rubber sheet behind one perforated plate to hold the pegs in place. It is hard to put the pegs in any intermediary positions in the rubber sheet
The devices of li and Jones use two parallel perforated plates with axially aligned apertures and plastic light conducting pegs. Li uses removable pegs which are frictionally held upon engaging the apertures in the rear plate. As with Lebensfeld's device, such pegs are capable of being easily misplaced due to their small size, or are even potentially hazardous if young children were to swallow them. Jones captures pegs between the perforated plates using a ridge around the center section of a peg. The ridge creates a peg diameter greater than the diameter of the apertures in the plates preventing the peg from being totally withdrawn from the plates. Jones uses a peg tapered on both ends to frictionally fit and stay in position. Li's and Jones' devices have only one or two positions in which an element is retained and thus also are not suitable if positions between those extremes are desired.